A while ago, a study showed that the female relatives of homosexual men tend to have more children than average females. The study suggested that male homosexuality could be due to androphilia genes rather than homosexuality genes. If we think this way, our chromosome system could explain why more males are homosexual.

Androphilia genes would survive through the females, but they would end up inside males too because females have no unique chromosome. On the other hand, males have a unique chromosome, the Y. Gynephilia genes on the Y chromosome would rarely end up in females. Thus there would be fewer female homosexuals.

My idea about homosexuality being more prevalent in males comes from the Kinsey Reports.

Also, if we think about sexual preference genes in terms of marginal utility, it would explain why gynephilia genes on other chromosomes would eventually be eliminated in favor of gynephilia genes on the Y chromosome.

http://econlib.org/library/Enc/Marginalism.htmlMarginal utility is the ecenomics concept that says individual things become less useful as you get more of that same thing. So if I have two buckets of water, I will use them on important things (i.e. those two buckets of water have a lot of utility). Fifty buckets of water would be uneccessary, so the average utility of each individual bucket would be lower.

I was overgeneralizing by saying that more men are homosexual. However, the data seem to indicate that more men engage in homosexual behavior. However, the terms "androphilia" and "gynephilia" indicate attraction, not behavior.

Examination of homosexual behavior separately finds that 6.2, 4.5, and 10.7% of males and 3.6, 2.1, and 3.3% of females in the United States, the United Kingdom, and France, respectively, report having had sexual contact with someone of the same sex in the previous 5 years.

In his classic survey research, Kinsey and his colleagues (1948) found that over a third of men and 13% of women in their sample had had at least one homosexual experience to orgasm. [...]a recent study of almost 5,000 twins in Australia found that although only 2.2% of the men and 0.6% of the women were exclusively homosexual, a much larger percentage—13% of men and 11% of women—had at least some sexual experience with, or attraction toward, the same sex (Zietsch et al., 2008).